Use of alkoxylated alkanolamide together with alkoxylated alcohol as a friction-reducing agent

ABSTRACT

Use of a mixture of at least one alkanolamide of general formula (I), wherein R is a hydrocarbon group having 7-23 carbon atoms, preferably 11-23 carbons atoms, A is an alkyleneoxy group having 2-4 carbon atoms and n is 2-12, preferably 2-8, and at least one alkoxylated alcohol in a weight ratio between the alkoxylated alkanolamide and the alkoxylated alcohol from 10:1 to 1:10, preferably in the range from 5:1 to 1:5 for producing a water-base liquid system with reduced flow resistance between the flowing, water-base liquid system and a solid surface.

This application is a 371 of PCT/EP96/00155, filed Jan. 9, 1996.

The present invention relates to the use of an alkoxylated alkanolamidetogether with an alkoxylated alcohol in a water-base system for reducingthe flow resistance between a solid surface and the water-base liquidsystem.

Surfactants with the ability to form extremely long, cylindricalmicelles have, in recent years, attracted a great interest asfriction-reducing additives to systems with circulating water,especially those destined for heat or cold distribution.

An important reason for this interest is that, although one desires tomaintain a laminar flow in the conduits, one wishes at the same time tohave turbulence in the heat exchangers to achieve therein a high heattransfer per unit area.

As may easily be understood, fibres or chain polymers are unable toprovide this double function which, however, can be achieved withrod-shaped micelles, since the flow rate (the Reynold's number) usuallyis much higher in the heat exchangers than in the conduit.

The rod-shaped micelles are distinguished by operating in a fairlydisorderly fashion at low Reynold's numbers (below 10⁴), having no oronly a very slight effect on the flow resistance.

At higher Reynold's numbers (above 10⁴), the micelles are paralleled andresult in a friction reduction very close to that which is theoreticallypossible.

At even higher Reynold's numbers (e.g. above (10⁵), the shear forces inthe liquid become so high that the micelles start to get torn and thefriction-reducing effect rapidly decreases as the Reynold's numberincreases above this value.

The range of Reynold's numbers within which the surface-active agentshave a maximum friction-reducing effect is heavily dependent on theconcentration, the range increasing with the concentration.

By choosing the right concentration of surface-active agents andsuitable flow rates in tubings and heat exchangers, it is thus possibleto establish a laminar flow in the tubes and turbulence in the heatexchangers. Thus, the dimensions of both the tubes and the exchangerscan be kept at a low level, or the number of pump stations, andconsequently the pump work, can alternatively be reduced while retainingthe same tubular dimensions.

The surface active agents most commonly used as friction-reducingadditives to circulating water systems for heat or cold distribution areof the type represented by alkyltrimethyl ammonium salicylate whereinthe alkyl group is a long alkyl chain which has 12-22 carbon atoms andwhich may either be saturated or contain one or more double bonds.

This type of surface-active agent functions satisfactorily already at aconcentration of 0.5-2 kg/m³, but is degraded very slowly, bothaerobically and anaerobically, and further is highly toxic to marineorganisms.

Since heat-distribution systems for small houses usually suffer fromimportant leaks (it is estimated that in one year 60-100 per cent of thewater leaks out), it follows that the added chemicals end up in theground water and in various fresh-water recipients. This combination oflow bio-degradability and high toxicity is a fundamental criterion for aproduct injurious to the environment.

Thus there is a general demand for surface-active agents which are lessharmful to the environment but which have the same excellent ability asthe quaternary ammonium compounds described above to reduce the flowresistance in circulating water systems.

In the U.S. Pat. No. 5,339,855 it is described that alkoxylatedalkanolamides with the general formula ##STR1## wherein R is ahydrocarbon group having 9-23 carbon atoms, A is an alkyleneoxy grouphaving 2-4 carbon atoms and n is 3-12, are capable of forming longcylindrical micelles in water and thus reduce the friction inwater-based system.

These products are easily degradable and function excellently indeionized water especially at low temperatures. However, thefriction-reducing effects are hampered in hard water and by the presenceof high amounts of electrolytes. Further the temperature range for theiroptimal friction-reducing effect will be rather narrow, sometimes assmall as 10° C.

In the U.S. Pat. No. 3,961,639 it is disclosed that a solution ofethoxylated fatty alcohols may have good friction-reducing propertieswhen it is tested at a temperature close to the cloud point of thesolution and when the surfactant concentration is at least 5 andpreferably 10 kg/m³.

We have now surprisingly found that a combination of alkoxylated fattyacid alkanolamides of formula I and an alkoxylated alcohol of theformula II

    R.sub.1 --(C.sub.r H.sub.2r O).sub.m H                     (II)

where R₁ is a saturated or unsaturated hydrocarbon group containing 8-24carbon atoms, m is a number from 1 to 12 and r a number from 2 to 4 withthe proviso that at least half of the alkyleneoxy units consists of C₂H₄ O units, will give water solutions with improved friction-reducingproperties at low temperatures within a rather wide temperature rangeboth below and above the cloud point of the solution in comparison withthe compounds forming the composition. Preferably the combination of thealkoxylated alkanolamide and the alkoxylated alcohol has a cloud pointbetween the highest and the lowest temperature for which the water-basesystem is intended. Furthermore, the crystallization temperature for thecombination is suitably below the lowest temperature for which thewater-base system is intended.

The mixtures according to the invention can also tolerate hard water andelectrolytes which may be added e.g. as corrosion inhibitors.

The weight ratio between the alkoxylated alkanolamide and thealkoxylated alcohol may be varied between 10:1 and 1:10, normallybetween 5:1 and 1:5. Besides the structure of the two surfactantcomponents the weight ratio will also depend significantly on thehardness and salt content of the water and the desired temperatureworking range for the solution.

The total amount of the alkoxylated alkanolamide and the alkoxylatedalcohol may vary within wide limits depending on the conditions, but isgenerally 0.1-10 kg/m³ of the water-base system.

By "water-base" is meant that at least 50 per cent by weight, preferablyat least 90 per cent by weight, of the water-base liquid system consistsof water.

The combination of alkoxylated alkanolamide and alkoxylated alcohol isespecially suited for use in water-base systems flowing in longconduits, e.g. circulating water systems for heat or cold distribution.

The alkoxylated alcohols according to the invention preferably containfrom 12 to 22 carbon atoms in the hydrocarbon group, while m preferablyis from 3 to 8 and r is 2.

The preferred alkoxylated alkanolamides for this invention contain 13-23carbon atoms in the hydrocarbon group, the alkyleneoxy group has 2carbon atoms and n is a number from 3 to 6. For cooling waterapplications when the water temperature is below 30° C. it is preferablethat at least a part of the hydrocarbon groups R and R₁ contain oneand/or more double bonds.

The alkoxylated alkanolamide can be produced by amidation of acarboxylic acid of the formula RCOOH, wherein R has the meaning statedabove, with an alkanolamine of the formula NH₂ AH, wherein A has themeaning stated above, or by aminolysis of a corresponding triglycerideor methyl ester with the abovementioned alkanolamine followed byalkoxylation of the resulting amide. The alkoxylation may be carried outin the presence of an alkaline catalyst at a temperature of 40-180° C.

It is especially suitable to carry out the alkoxylation in the presenceof a tertiary amine lacking protons that react with alkylene oxide, oran alkylene-oxide-quaternised derivative of the tertiary amine at atemperature ranging from room temperature to 120° C., which results inhigh yields of the desired product. Suitable teritary amines includetrimethylamine, triethylamine, tributylamine, dimethyloctylamine,tetramethylethylenediamine, dimethyl coconut amine, tristearyl amine,dimethyl piperazine and diazabicyclooctane.

The alkoxylation may comprise ethoxylation, propoxylation, addition ofpropylene oxide in blocks, simultaneous addition of ethylene oxide andpropylene oxide, or a combination thereof. The ethylene oxideconveniently amounts to at least 50 mole per cent of the added alkyleneoxide. To use only ethoxylation is preferred.

The carboxylic acids of the formula RCOOH, wherein R has the meaningstated above, may be aliphatic, aromatic as well as cyclo-aliphatic.Suitable carboxylic acids include the aliphatic carboxylic acids inwhich the hydrocarbon part may be saturated or unsaturated, straight orbranched. To use conventional fatty acids is especially preferred.

Suitable alkoxylated alkanolamides include the following specificexamples: ##STR2## wherein ##STR3## is derived from rape seed oil fattyacid, ##STR4## wherein ##STR5## is derived from rape seed oil fattyacid, ##STR6## wherein ##STR7## is derived from lauric acid, ##STR8##wherein ##STR9## is derived from lauric acid, ##STR10## wherein##STR11## is derived from stearic acid, and the group A is random addedfrom equal mole parts of ethylene oxide and propylene oxide ##STR12##wherein ##STR13## is derived from linolenic acid.

The choice of chain length and degree of unsaturation is determined bythe temperature range in which the alkoxylated alkanolamide is tooperate but also by the kind and amount of the alkoxylated alcohol whichwill be included in the mixture and the hardness and salt content of thewater which shall be used for the solution.

The general principle is then that a hydrophobic alkoxylatedalkanolamide, i.e. with a large hydrocarbon group and a low degree ofalkoxylation will need a rather hydrophilic alkolylated alcohol i.e.with a short to moderate hydrocarbon group and a moderate to largealkyleneoxy group which mainly should consist of ethyleneoxy units. Thealkoxylated alcohol may also contain two or more alkyleneoxy groups.

The use of hard or salt water will have the same effect as making thealkoxylated alkanolamide more hydrophobic, i.e. it creates a demand foreither a higher amount of the alkoxylated alcohol or a more hydrophilicsurfactant of this type. A convenient way to find out the rightproportion between the alkoxylated alcohol and the alkoxylatedalkanolamide is to disperse the latter in the water having the highesttemperature in the planned operational temperature range and then addsuccessively a solution of the former surfactant until the dispersedalkoxylated alkanolamide just has been solubilized.

Suitable alkoxylated alcohols according to the invention are ethoxylatedfatty alcohols where the alcohols have been produced from fatty acids orfatty acid esters or by hydroformulation of olefins by a so-calledOxo-process. The hydrocarbon group in the alcohol may be branched orunbranched, saturated or unsaturated and the choice will be determinedby the temperature working range for which the final product is intendedwhere branched or unsaturated groups are preferred for low-temperaturework i.e. for cooling water.

Apart from the alkoxylated alkanolamide and the alkoxylated alcohol thewater-base system may contain a number of conventional components, suchas rust-preventing agents, anti-freeze, and bactericides. The system mayalso include solubilisers, such as diethylene glycol monobutyl ethers,which may affect the cloud-point of the surfactant mixture in thewater-base system quite considerably.

The present invention will now be further illustrated with the aid ofthe following examples.

EXAMPLES

The friction-reducing properties of the compositions and productsaccording to the prior art have been tested according to two differentmethods, one rather simple procedure, which will be called the screeningtest, and one more elaborated streaming test, which will be called theloop test.

Screening test

A series of 50 ml glass beakers of the same dimensions (65×35 mm) eachcontaining a Teflon-covered cylindrical magnet (20×6 mm) were eachfilled with 40 ml test solution and then kept in a refrigerator at least4 h at 3° C. The beakers were then taken out one by one, immediatelyplaced on a magnetic stirrer, a thermometer immersed to a depth of 15mm, the stirrer started at full speed, 1400 rpm, and the depth of thevortex formed in the solution was recorded at various temperatures whilethe solution temperature increased to room temperature during 15 mins.

When no vortex could be detected (recorded as 0 mm), it is known byexperience that this indicates good friction reducing properties.

If on the other hand no efficient additive was present, e.g. for purewater the vortex reached down to the stirring magnet and the result wasrecorded as 35 mm.

Loop test

Measurements were carried out in a 6 m tube loop consisting of twostraight and stainless tubes (3 m each), one tube having an innerdiameter of 8 mm and the other having an inner diameter of 10 mm. Waterwas pumped through the tube loop by a centrifugal pump, which was drivenby a frequency-controlled motor for continuous adjustment of the flowrate, which was determined by a rotameter.

The straight parts of the tube loop had outlets which, with the aid ofvalves, could in turn be connected to a differential pressure gaugewhose other side was all the time connected to a reference point in thetube loop. Further, the tube loop was heat-insulated, and the suctionside of the pump was connected to a thermostatically controlledcontainer with a volume of 20 l, to which the return flow from the tubeloop was directed.

After the test compound had been added and the aqueous solution had beenthermostatically controlled, measurements began at low flow rates, andthe pressure difference from two points on the 10 mm tube and threepoints on the 8 mm tube were measured for each flow rate. The pressuredifferences thus measured were then converted into Moody's frictionfactory Y and are shown in the examples as a function of the Reynold'snumber Re.

Y=2D.P_(diff) /V².L.d

Re=D.V.d/u

D=tube diameter

V=flow rate

L=tube length over which the pressure difference P_(diff) was measured

d=density of the liquid

u=viscosity of the liquid

The examples also state the corresponding Prandtl number and Virknumber. The former corresponds to the friction factor of water only,i.e. with turbulence, and the latter corresponds to flow withoutturbulence, i.e. a laminar flow.

Examples 1-3

These examples were carried out according to the screening testdescribed previously.

The alkoxylated alkanolamides used in these examples weremonoethanolamides of technical oleic acid to which had been added 3; 4;5; and 6 moles of ethylene oxide. These products will in the followingbe called OMA-3; OMA-4 etc. The technical oleic acid consists of 60percent oleic acid, 20 percent linoleic acid and 10 percent linolenicacid, the rest being mainly palmitic and stearic acids.

As alkoxylated alcohol in these examples has been used the reactionproduct of 1 mol technical oleyl alcohol with an iodine number of 85 and6 moles of ethylene oxide with KOH as a catalyst. This product ishereafter called OLA-6.

The water used in these examples was a hard water containing 2.2 molesCa²⁺ and 1.4 moles Mg²⁺ per m³ and as a corrosion inhibitor 1.3 kgNaNO₂, 0.35 kg NaNO₃ and 0.35 kg NaBO₂.4 H₂ O per m³.

The composition of the test solutions are given in the table below:

    ______________________________________                                                OMA-3  OMA-4    OMA-5    OMA-6 OLA-6                                  Test solution                                                                           All conc. given in kg a.s.*.sup.) per m.sup.3                       ______________________________________                                        I         0.80     --       --     --    3.50                                   II -- 2.00 -- -- 2.00                                                         III -- -- 2.00 -- 2.00                                                        Comparison 1 -- -- -- -- 4.00                                                 Comparison 2 -- 1.60 -- 2.40 --                                             ______________________________________                                         *.sup.) a.s. = active substance                                          

The test results are given as the depth of the vortex formed in mm atthe stirrer speed of 1400 rpm.

    ______________________________________                                                Temperature, ° C.                                              Test solution                                                                           3      5      8     12   14   18   20                               ______________________________________                                        I          2*     2*     3*    3*   4*   4*   4*                                II  0 0 2  3*  5* 10* 10*                                                     III  0 0 0 1  2*  4*  5*                                                      Comparison I 20 20  20  13  2 2 2                                             Comparison II 15 5 0 1 3 10  10                                             ______________________________________                                         The asterisk * means that the solution was turbid.                       

The results of these tests indicate that the compositions according tothe invention have a significant stabilizing effect on the water inimmediate vicinity of a turbulent zone and have thus a goodfriction-reducing ability on water flowing in a tube, especially at lowtemperatures. The comparison tests show that the ethoxylated alcohol hasonly a limited friction-reducing effect at temperatures below 14° C.,while the ethoxylated ethanolamides in Comparison II show an excellentfriction-reducing effect only within a narrow temperature interval(8-14° C.).

Examples 4-6

These examples were carried out according to the loop test. The waterused had the same composition as the water in Examples 1-3. Thesurfactants added were 3.00 kg/m³ of OMA-5 and 3.00 kg/m³ of OLA-6 wherethe acronyms OMA-5 and OLA-6 has the same meaning as in Examples 1-3.

Example 4

Water temp. 6.4° C., pH 9.5, cloud point 12° C.

    ______________________________________                                        Moody's friction factor × 10.sup.3                                      ______________________________________                                        Reynolds                                                                             3 × 10.sup.3                                                                    5 × 10.sup.3                                                                    10.sup.4                                                                          2 × 10.sup.4                                                                  3 × 10.sup.4                                                                  4 × 10.sup.4                                                                  6 × 10.sup.4                 number                                                                        Prandtl 45 38 32 27 24 22 20                                                  number                                                                        10 mm 50 30 19 18 14 16 20                                                    tube                                                                          8 mm 47 23 10 11 12 15 18                                                     tube                                                                          Virk 25 18 11 7 6 5 4.5                                                       number                                                                      ______________________________________                                    

Example 5

Water temp. 11° C., pH 9.5, cloud point 12° C.

    ______________________________________                                        Moody's friction factor × 10.sup.3                                      ______________________________________                                        Reynolds                                                                             3 × 10.sup.3                                                                    5 × 10.sup.3                                                                    10.sup.4                                                                          2 × 10.sup.4                                                                  3 × 10.sup.4                                                                  4 × 10.sup.4                                                                  6 × 10.sup.4                 number                                                                        Prandtl 45 38 32 27 24 22 20                                                  number                                                                        10 mm 43 32 17 11 7 7 12                                                      tube                                                                          8 mm 42 25 12 10 7 5 11                                                       tube                                                                          Virk 25 18 11 7 6 5 4.5                                                       number                                                                      ______________________________________                                    

Example 6

Water temp. 20.5° C., pH 9.5, cloud point 12° C.

    ______________________________________                                                Moody's friction factor × 10.sup.3                              ______________________________________                                        Reynolds                                                                             3 × 10.sup.3                                                                    5 × 10.sup.3                                                                    10.sup.4                                                                          2 × 10.sup.4                                                                  3 × 10.sup.4                                                                  4 × 10.sup.4                                                                  6 × 10.sup.4                 number                                                                        Prandtl 45 38 32 27 24 22 20                                                  number                                                                        10 mm 55 30 13 10 8 6 5                                                       tube                                                                          8 mm 35 23 11 8 6 5 5                                                         tube                                                                          Virk 25 18 11 7 6 5 4.5                                                       number                                                                      ______________________________________                                    

From these three loop tests with a composition according to theinvention it can clearly be seen that a substantial friction-reducingeffect can be achieved in the temperature range 6-21° C. in a hard watercontaining added salts and with a dosage of 6.0 kg per m³.

We claim:
 1. A method for reducing the flow resistance between aflowing, water-based liquid system and a solid surface which comprisesadding to said liquid system at least one alkoxylated alkanolamide ofthe general formula ##STR14## wherein R is a hydrocarbon group having7-23 carbon atoms, A is an alkyleneoxy group having 2-4 carbon atoms andn is 2-12, and at least one alkoxylated alcohol of the formula

    R.sub.1 --(C.sub.r H.sub.2r O).sub.m H                     (II)

where R₁ is a saturated or unsaturated hydrocarbon group containing 8-24carbon atoms, m is a number from 1 to 12 and r a number from 2 to 4 withthe proviso that at least half of the alkyleneoxy units consist of C₂ H₄O units, in a weight ratio between the alkoxylated alkanolamide and thealkoxylated alcohol from 10:1 to 1:10.
 2. The method of claim 1, whereinthe combination of the alkoxylated alkanolamide and the alkoxylatedalcohol has a cloud point between the highest and the lowest temperaturefor which the water-base system is intended.
 3. The method of claim 1wherein the crystallization temperature for the mixture is below thelowest temperature for which the water-based system is intended.
 4. Themethod of claim 1 wherein the water-based system is a cooling mediumwith a temperature below 30° C.
 5. The method of claim 1 wherein themixture of alkoxylated alkanolamide and alkoxylated alcohol is added inan amount of 0.1-10 kg/m³ of the water-base system.
 6. The method ofclaim 1 wherein at least half of the alkyleneoxy groups in thealkoxylated alkanolamide are ethyleneoxy groups.
 7. The method of claim6 wherein A is an ethyleheoxy group.
 8. The method of claim 1 wherein atleast half of the groups C_(r) H_(2r) O in the alkoxylated alcohol areethyleneoxy groups.
 9. The method of claim 8 wherein all alkyleneoxygroups are ethyleneoxy groups.
 10. The method of claim 1 wherein atleast a part of the hydrocarbon groups R and R₁ contain one and/or moredouble bonds.
 11. The method of claim 1 wherein the weight ratio betweenthe alkoxylated alkanolamide and the alkoxylated alcohol is in the rangeof from 5:1 to 1:5.
 12. The method of claim 1 wherein R is a hydrocarbonhaving 11-23 carbon atoms and n is 2-8.